Fluoride phosphor and light-emitting device using same

ABSTRACT

Provided is a fluoride phosphor that has a good external quantum efficiency and is suitable for stably producing white LEDs. The fluoride phosphor having a composition represented by a general formula (1), a bulk density of 0.80 g/cm 3  or more, and a mass median diameter (D50) of 30 μm or less: general formula: A 2 M (1−n) F 6 :Mn 4+   n  
         (1), wherein 0&lt;n≤0.1, the element A is one or more alkali metal elements including at least K, and the element M is a simple substance of Si, a simple substance of Ge, or a combination of Si and one or more elements selected from the group consisting of Ge, Sn, Ti, Zr, and Hf.

TECHNICAL FIELD

The present invention relates to a fluoride phosphor that is excited byblue light and emits red light, and a light emitting device using thesame.

BACKGROUND ART

In recent years, white light emitting diodes (white LEDs), which are acombination of a light emitting diode (LED) and a phosphor, have beenapplied as white light sources to backlight light sources and lightingdevices of displays. Among them, white LEDs using InGaN blue LEDs asexcitation sources are widely used.

The phosphor used for the white LED needs to be excited efficiently bythe light emission of the blue LED and to emit visible lightfluorescence. A typical example of the phosphor for white LED includes aCe-activated yttrium aluminum garnet (YAG) phosphor that is efficientlyexcited by blue light and exhibits broad yellow light emission. A pseudowhite color is obtained by combining a YAG phosphor singly with a blueLED and exhibits light emission in a wide visible light region. For thisreason, the white LED including a YAG phosphor is used for lighting andbacklight sources, but few red components cause problems that colorrendering is low for lighting applications and color reproduction rangeis narrow for backlight applications.

For the purpose of improving color rendering and color reproducibility,a white LED combining a red phosphor capable of being excited by a blueLED and a green phosphor such as Eu-activated β-sialon or orthosilicatehas also been developed.

As a red phosphor for such a white LED, a nitride or an oxynitridephosphor with Eu²⁺ as the emission center is widely used because of highfluorescence conversion efficiency, small brightness loss at hightemperature, and excellent chemical stability, and typical examplesthereof include phosphors represented by the chemical formulas,Sr₂Si₅N₈:Eu²⁺, CaAlSiN₃:Eu²⁺, and (Ca, Sr) AlSiN₃:Eu²⁺. However, theemission spectrum of the phosphor using Eu²⁺is broad and includes manylight emitting components with low visibility, and hence the brightnessof the white LED is significantly reduced as compared with the case ofsingly using the YAG phosphor regardless of high fluorescence conversionefficiency. In addition, the phosphor particularly used for displaysrequires the compatibility of the combination of color filters, causingthe following problem: the phosphor having broad emission spectrum (notbeing sharp) is not preferable.

Examples of the emission center of the red phosphor having a sharpemission spectrum include Eu³⁺ and Mn⁴⁺. Among them, the red phosphorobtained by activating with dissolving Mn⁴⁺ in a fluoride crystal suchas K₂SiF₆ is efficiently excited by blue light and has a sharp emissionspectrum with a narrow half-value width. Thus, excellent color renderingand color reproducibility may be realized without lowering thebrightness of the white LED, and in recent years, application of theK₂SiF₆:Mn⁴⁺ phosphor to the white LED has been actively investigated(refer to Non Patent Literature 1).

Patent Literature 1 discloses a fluoride phosphor having a predeterminedcomposition including silicon and having a weight median diameter of 35μm or more and a bulk density of 0.80 g/cm³ or more.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No. 6024850

Non Patent Literature

-   Non Patent Literature 1: A. G. Paulusz, Journal of The    Electrochemical Society, 1973, Volume 120, issue 7, p. 942-947

SUMMARY OF INVENTION Technical Problem

In light emitting devices such as backlights of liquid crystal displaysand lighting fixtures, improvement of light emission characteristics isalways required, and hence, improvement of characteristics of eachmember is required, and phosphors are also required to improve lightemission characteristics. The white LED using a K₂SiF₆:Mn⁴⁺ phosphor hasthe following problem: the light emission characteristics varysignificantly.

The present inventors have found that even the fluoride phosphordisclosed in the above Patent Literature 1 causes the following problem:sufficient brightness actually fails to be obtained stably and the yieldas white LED products is bad.

For this reason, there is a demand for the fluoride phosphor that hasgood external quantum efficiency and is suitable for stably producingwhite LEDs.

Solution to Problem

As a result of various investigations on the physical properties of thefluoride phosphor, the present inventors have found that using fluoridephosphors having specific powder characteristics may stably producewhite LEDs with excellent external quantum efficiency, and have reachedthe present invention.

That is, the present invention provides the following.

[1]

A fluoride phosphor having a composition represented by the followinggeneral formula (1), a bulk density of 0.80 g/cm³ or more, and a massmedian diameter (D50) of 30 μm or less:

General formula: A₂M_((1−n))F₆:Mn⁴⁺ _(n)  (1)

wherein 0<n≤0.1; an element A is one or more alkali metal elementscontaining at least K; an element M is a simple substance of Si, asimple substance of Ge, or a combination of Si and one or more elementsselected from the group consisting of Ge, Sn, Ti, Zr, and Hf.[2] The fluoride phosphor according to [1], wherein in the generalformula (1), the element A is a simple substance of K and the element Mis a simple substance of Si.[3]

The fluoride phosphor according to [1] or [2], wherein the bulk densityis 0.80 g/cm³ or more and 1.40 g/cm³ or less.

[4]

The fluoride phosphor according to [1] to [3], wherein the mass mediandiameter is 15 μm or more and 30 μm or less.

[5]

The fluoride phosphor according to [1] to [4], wherein a span value is1.5 or less, as calculated by a formula (2) using a 10% diameter (D10)and a 90% diameter (D90) obtained from a mass-based cumulativedistribution curve and the mass median diameter (D50).

Formula: (span value)=(D90−D10)/D50  (2)

[6]

The fluoride phosphor according to [1] to [5], wherein an angle ofrepose is 30° or more and 60° or less.

[7]

A light emitting device comprising:

the fluoride phosphors according to [1] to [6] and a light emittingsource.

[8]

The light emitting device according to [7], wherein a peak wavelength ofthe light emitting source is 420 nm or more and 480 nm or less.

[9]

The light emitting device according to [7] or [8], wherein the lightemitting device is a white LED device.

Advantageous Effects of Invention

The present invention may provide a fluoride phosphor suitable forstable production of white LEDs having good light emissioncharacteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows comparison of the X-ray diffraction pattern of the phosphorobtained in Example 1 with that of K₂SiF₆ (ICSD-29407) which isComparative Example 1 and a control. The vertical axis in the figurerepresents the number of the count of the signal.

FIG. 2 shows excitation and fluorescence spectra of the phosphorobtained in Example 1.

FIG. 3 is a frequency distribution curve of the phosphor according toExamples 1 to 2 and Comparative Examples 1 to 2.

FIG. 4 is a cumulative distribution curve of the phosphor according toExamples 1 to 2 and Comparative Examples 1 to 2.

DESCRIPTION OF EMBODIMENTS

in the present specification, unless otherwise specified, when anumerical range is indicated, the upper limit value and the lower limitvalue are included.

The present invention is a fluoride phosphor represented by the generalformula: A₂M_((1−n))F₆:Mn⁴⁺ _(n). In the general formula, the element Ais an alkali metal element including at least potassium (K), andspecifically is a simple substance of potassium or a combination ofpotassium and at least one or more alkali metal elements selected fromlithium (Li), sodium (Na), rubidium (Rb), and cesium (Cs). From theviewpoint of chemical stability, the content of potassium in the elementA is preferably higher, and most preferably, a simple substance ofpotassium may be used as the element A.

In the general formula, the element M is a tetravalent element includingat least silicon (Si), and specifically is a simple substance ofsilicon, a simple substance of germanium (Ge), or a combination ofsilicon and one or more elements selected from the group consisting ofgermanium, tin (Sn), titanium (Ti), zirconium (Zr), and hafnium (Hf).From the viewpoint of chemical stability, the content of silicon in theelement M is preferably higher, and most preferably, a simple substanceof silicon may be used as the element M. In the general formula, F isfluorine and Mn is manganese.

The bulk density of the fluoride phosphor according to the embodiment ofthe present invention is required to be 0.80 g/cm³ or more. The bulkdensity is less than 0.80 g/cm³, reducing the external quantumefficiency and resulting in the large variation in the external quantumefficiency of the LED produced by using this phosphor. In a preferableembodiment, the bulk density may be in the range of 0.80 g/cm³ or moreand 1.40 g/cm³ or less, more preferably in the range of 0.90 g/cm³ ormore and 1.40 g/cm³ or less, and still more preferably in the range of1.00 g/cm³ or more and 1.30 g/cm³ or less. Too high bulk density tendsto result in large variation in the external quantum efficiency of theLED, and hence the performance may be inferior.

The bulk density may vary depending on the state of the powder surfaceand the post-treatment method during manufacturing, and is notimmediately determined from the only particle size distribution. Thatis, the present invention is based on the effect obtained from a novelcombination of a predetermined bulk density and mass median diameter.

The fluoride phosphor according to the embodiment of the presentinvention is required to have a mass median diameter (D50) of 30 μm orless, measured by a laser diffraction scattering method. The mass mediandiameter of more than 30 μm causes the problems of deterioration ofdispersibility in an encapsulation resin in manufacturing a white LED,lower brightness, and lower manufacturing stability. In a preferableembodiment, the mass median diameter may be in the range of 15 μm ormore and 30 μm or less, more preferably in the range of 16 μm or moreand 29 μm or less. In the present specification, the mass mediandiameter is a value converted and calculated from a volume mediandiameter obtained from a cumulative distribution curve measured by alaser diffraction scattering method in accordance with JIS R1622: 1995and P1629: 1997. Too small mass median diameter may reduce the externalquantum efficiency.

The fluoride phosphor according to the embodiment of the presentinvention preferably further has the span value of 1.5 or less. In thepresent specification, the span value means a value calculated by(D90-D10)/D50, wherein D10 and D90 are a 10% diameter and a 90% diameterobtained from a mass-based cumulative distribution curve measured in thesame manner as the above mass median diameter. The span value is anindex representing the distribution width of the particle sizedistribution, that is, the variation in the size of the fluoridephosphor particles. Too large span value tends to result in largervariation in the external quantum efficiency of the produced LED. Thatis, a span value of 1.5 or less results in sharp distribution of theparticle size of the fluoride phosphor, meaning to have thecharacteristics that the particles are uniform as a powder, and it isassumed that the effect of further improving dispersibility in theencapsulation resin may be exhibited. In a preferable embodiment, thespan value may be in the range of 0.1 or more and 1.4 or less, in therange of 0.1 or more and 1.3 or less, in the range of 0.1 or more and1.2 or less, in the range of 0.1 or more and 1.1 or less, or in therange of 0.1 or more and 1.0 or less.

In the fluoride phosphor according to the embodiment of the presentinvention, furthermore, the mass-based frequency distribution curve ispreferably unimodal. The single peak (mode diameter) is more preferably10 μm or more, and furthermore preferably 10 μm or more and 100 μm.

In the fluoride phosphor according to the embodiment of the presentinvention, the repose angle measured in accordance with JIS P9301-2-2:1999 is preferably 30° or more and 60° or less. The repose angleindicates the fluidity of the fluoride phosphor, that is, an indexrepresenting the degree of dispersion when the fluoride phosphor is usedin an LED. A repose angle of less than 30° or more than 60° may tend toresult in larger variation in the external quantum efficiency of theproduced LED.

In a preferable embodiment, the fluoride phosphor may have a combinationof a bulk density of 0.80 g/cm³ or more, a mass median diameter of 30 μmor less, a span value of 1.5 or less, and a repose angle of 30° to 60°.In a more preferable embodiment, the fluoride phosphor may also have acombination of a bulk density of 0.80 g/cm³ to 1.40 g/cm³, a mass mediandiameter of 15 μm to 30 μm, a span value of 1.5 or less, and a reposeangle of 30° to 60°.

The fluoride phosphor according to the embodiment of the presentinvention may be prepared by, for example, a method including thefollowing steps so as to have predetermined powder characteristics (suchas bulk density and mass median diameter). A step of mixing hydrofluoricacid and a compound of an alkali metal hydrofluoride to obtain asolution. A step of adding a tetravalent element oxide and a compound ofan alkali metal hexafluoromanganate to the solution to obtain aprecipitate. A step of collecting, washing, and drying the precipitateto obtain a fluoride phosphor (powder).

Adjustment of powder characteristics may be controlled by the blendingratio of the hydrofluoric acid, the compound of the alkali metalhydrofluoride, the oxide of the tetravalent element, and the compound ofthe alkali metal hexafluoromanganate described above, or the additionrate of the oxide of the tetravalent element and the compound of thealkali metal hexafluoromanganate. Generally, in the field of phosphors,it is known that the physical properties (such as a form as a substanceand peak wavelength and spectrum shape of emission spectrum) aredifferent depending on the different main components of the phosphor.That is, it should be noted that the fluoride phosphor according to anembodiment of the present invention naturally exhibits completelydifferent behavior when used in a light emitting device even if thepowder characteristics are apparently the same as other phosphors suchas a YAG phosphor and a sialon phosphor.

The obtained fluoride phosphor powder may be further classified by usingmeans such as a sieve or a classifier and adjusted so as to obtaindesired powder characteristics. In addition, the above step group ispreferably performed at normal temperature. In the presentspecification, “normal temperature” refers to a temperature rangedefined by JIS Z8703: 1983, that is, a temperature in a range of 20±15°C.

In the embodiment of the present invention, a light emitting device(such as an LED) including the above fluoride phosphor and a lightemitting source may be also provided. In such a light emitting device,the fluoride phosphor is preferably used by encapsulating it in aencapsulant. Such an encapsulant is not particularly limited, andexamples thereof include silicone resin, epoxy resin, perfluoropolymerresin, and glass. In applications requiring high output and highbrightness, such as display backlight applications, an encapsulanthaving durability against exposure to even high temperatures or intenselight is preferable, and from the viewpoint of this, a silicone resin isparticularly preferable.

The light emitting source is preferable to emit light having awavelength that complements the red light emission of the fluoridephosphor or light having a wavelength that may efficiently excite thefluoride phosphor, and for example, a blue light source (such as blueLED) may be used. Preferably, the peak wavelength of light from thelight emitting source may be a wavelength in a range including blue (forexample, a range of 420 nm or more and 560 nm or less), and morepreferably a range of 420 nm or more and 480 nm or less.

EXAMPLES

Hereinafter, the present invention is described in more detail withreference to Examples and Comparative Examples of the present invention.

<Manufacturing Step of K₂MnF₆>

K₂MnF₆ used for performing the manufacturing methods of the fluoridephosphors in Examples and Comparative Examples was prepared according tothe method described in Non Patent Literature 1. Specifically, 800 ml of40% hydrofluoric acid by mass was placed in a fluororesin beaker havinga capacity of 2000 ml, and 260.00 g of potassium hydrogen fluoridepowder (manufactured by Wako Pure Chemical Industries, Ltd., guaranteedreagent) and 12.00 g of potassium permanganate powder (manufactured byWako Pure Chemical Industries, Ltd., the first grade reagent) weredissolved. While stirring this hydrofluoric acid solution with amagnetic stirrer, 8 ml of a 30% hydrogen peroxide solution (guaranteedreagent) was dropped in portions. When the dropping amount of thehydrogen peroxide solution exceeded a certain amount, a yellow powderstarted to deposit and the color of the reaction solution started tochange from purple. A certain amount of the hydrogen peroxide solutionwas dropped, and then stirring was continued for a while, and thenstirring was stopped to precipitate a deposited powder. After theprecipitation, the supernatant was removed, methanol was added, stirred,left, the supernatant was removed, and methanol was further added, andthis operation was repeated until the solution became neutral.Thereafter, the deposited powder was collected by filtration, furtherdried, and methanol was completely removed by evaporation to obtain19.00 g of K₂MnF₆ powder. All these operations were performed at normaltemperature.

Example 1

As Example 1, a method of manufacturing a fluoride phosphor representedby K₂SiF₆:Mn is shown below. Under normal temperature, 200 ml of 55%hydrofluoric acid by mass was placed in 500 ml of a fluororesin beaker,and 25.5 g of KHF₂ powder (manufactured by Wako Pure ChemicalIndustries, Ltd., guaranteed reagent) was dissolved to prepare anaqueous solution (B). To this solution, 6.9 g of silica (SiO₂, tradename FB-50, manufactured by Denka Company Limited) and 1.1 g of K₂MnF₆powder were added. When silica powder was added to the aqueous solution,the temperature of the aqueous solution increased due to the generationof heat of dissolution. The solution temperature reached the maximumtemperature about 3 minutes after the addition of silica, and then thesolution temperature decreased because dissolution of the silica wascompleted. It was visually confirmed that yellow powder started to formin the aqueous solution immediately after silica powder was added.

The silica powder was completely dissolved, and then the aqueoussolution was stirred for a while to complete the deposition of theyellow powder, and then the aqueous solution was left to stand toprecipitate a solid substance. After confirming the precipitation, thesupernatant was removed, and the yellow powder was washed withhydrofluoric acid having a concentration of 20% by mass and methanol,and this was further filtered to separate and collect the solidsubstance, and the remaining methanol was removed by evaporation througha drying treatment. After the drying treatment, a nylon sieve having anopening of 75 μm was used, and only the yellow powder that passedthrough this sieve was classified and collected to finally obtain 19.8 gof yellow powder.

<Confirmation of Yellow Powder Mother Crystal by Crystal PhaseMeasurement>

For the yellow powder obtained in Example 1, the X-ray diffractionpattern was measured by using an X-ray diffractometer (trade nameUltima4, manufactured by Rigaku Corporation, CuKα tube bulb was used).The obtained X-ray diffraction pattern is shown in FIG. 1. As a result,the X-ray diffraction pattern of the sample obtained in Example 1 wasthe same pattern as that of the K₂SiF₆ crystal, confirming thatK₂SiF₆:Mn was obtained in a single phase.

Example 2 and Comparative Examples 1 to 4

Example 2 and Comparative Examples 1 to 4 were obtained in the samemanner as in Example 1, except that the blending composition in Example1 was changed to the formulation shown in Table 1 below. X-raydiffraction patterns were measured for the obtained yellow powders, allof which showing the same pattern as the K₂SiF₆ crystal.

TABLE 1 Hydrofluoric acid KHF₂ SiO₂ K₂MnF₆ (ml) (g) (g) (g) Example 1200 25 5 6.9 1.1 Example 2 200 35.2 6.9 1.1 Comparative 200 25.5 13.11.1 Example 1 Comparative 200 20.7 6.9 1.1 Example 2 Comparative 20025.5 10.0 1.1 Example 3 Comparative 200 23.9 6.9 1.1 Example 4

<Evaluation of Light Emission Characteristics of Fluoride Phosphor>

The light emission characteristics of the fluoride phosphors in Examples1 and 2 and Comparative Examples 1 to 4 were evaluated by measuring theabsorption rate, internal quantum efficiency, and external quantumefficiency by the following methods. That is, a standard reflector plate(trade name Spectralon, manufactured by Labsphere, Inc.) having areflectance of 99% was set in the side opening (ϕ10 mm) of theintegrating sphere (ϕ60 mm). Monochromatic light separated at awavelength of 455 nm from a light emitting source (Xe lamp) wasintroduced into this integrating sphere with an optical fiber, and thespectrum of reflected light was measured with a spectrophotometer (tradename MCPD-7000, manufactured by Otsuka Electronics Co., Ltd.). At thetime, the excitation light photon number (Qex) was calculated from thespectrum in the wavelength range of 450 to 465 nm. Next, a concave cellfilled with a phosphor so as to obtain a smooth surface was set in theopening of the integrating sphere and irradiated with monochromaticlight with a wavelength of 455 nm, and the excitation reflected lightand fluorescence spectra were measured with the spectrophotometer. Anexcitation and fluorescence spectrums obtained from the fluoridephosphor in Example 1 are shown in FIG. 2 as a representative. Thephoton number of excitation and reflection light (Qref) and thefluorescence photon number (Qem) were calculated from the obtainedspectrum data. The photon number of excitation and reflection light wascalculated in the same wavelength range as the excitation light photonnumber, and the fluorescent photon number was calculated in the range of465 to 800 nm. From the obtained three types of photon numbers, externalquantum efficiency (=Qem/Qex×100), absorption rate(=(Qex−Qref)/Qex×100), and internal quantum efficiency(=Qem/(Qex−Qref)×100) were determined.

<Bulk Density of Fluoride Phosphor>

The bulk density of each of the fluoride phosphors in Examples 1 to 2and Comparative Examples 1 to 4 was evaluated in accordance with JIS R1628: 1997. That is, a constant volume container (100 cc) was used as ameasurement container, and its mass was measured with a scale. Thesample was placed in the measurement container through a sieve until itoverflowed, while taking sufficient care not to apply vibration orpressure. The powder rising from the upper end surface of themeasurement container was leveled off using a leveling plate. At thetime, the leveling plate was used by being inclined backward from thedirection of leveling so as not to compress the powder. The mass of themeasurement container was weighed with a scale, and the mass of thesample was calculated by subtracting the mass of the measurementcontainer. This measurement was performed three times. The average valueof the values obtained by dividing the mass of the sample calculated ineach measurement by the volume of the measurement container wascalculated as the bulk density.

<Evaluation of Mass Median Diameter and Span Value of Fluoride Phosphor>

The mass median diameters of the fluoride phosphors in Examples 1 and 2and Comparative Examples 1 to 4 were evaluated by the following methods.That is, 30 ml of ethanol was weighed in a 50 ml beaker, and 0.03 g of aphosphor was placed therein. Nest, this container was set in ahomogenizer (trade name US-150E, manufactured by Nippon Seiki SeisakushoCo., Ltd.) whose output was adjusted to “Altitude: 100%” in advance, andpretreatment was performed for 3 minutes. For the solution prepared asdescribed above, D10, D50 (mass median diameter), D90, and D100 weredetermined by using a laser diffraction/scattering particle sizedistribution analyzer (trade name MT3300EXII, manufactured byMicrotrackBell Corporation). D100 means a 100% diameter obtained from amass-based cumulative distribution curve measured in the same manner asthe above mass median diameter.

<Evaluation of Repose Angle of Fluoride Phosphor>

The repose angle of each fluoride phosphor in Examples 1 and 2 andComparative Examples 1 to 4 was evaluated by an injection method inaccordance with JIS R 9301-2-2: 1999. That is, from the height of 2 to 4cm of the upper edge of a commercially available glass funnel having anozzle inner diameter of 6 mm, 200 g of the powder to be measured wasdropped onto the substrate through the funnel at a rate of 20 to 60 gper minute, and from the diameter and height of the generated conicaldeposit, the repose angle was calculated.

The evaluation result of each fluoride phosphor in Examples 1 and 2 andComparative Examples 1 to 4 is summarized in Table 2 below. In thisresult, the span value was calculated as (D90-D10)/D50 using D10, D50,and D90 obtained above. In Comparative Examples 3 to 4, D100 was failedto be measured. FIG. 3 also shows a graph of cumulative distributiondata in Examples 1 to 2 and Comparative Examples 1 to 2. It may beunderstood that the cumulative distribution curves in Examples 1 and 2are steeper than those in Comparative Examples 1 and 2. Furthermore, thefrequency distribution curves in Examples 1 to 2 and ComparativeExamples 1 to 2 are also shown in FIG. 4, and it is also understood thata unimodal and sharp peak is obtained in Examples and is not obtained inComparative Examples. These results suggest that the uniformity of theparticle size in Examples is higher than that in Comparative Examples.

TABLE 2 Optical characteristics (455 nm excitation, unit: %) Particlesize Absorbance Internal quantum External quantum Bulk densitydistribution (μm) Span Repose ratio efficiency efficiency (g/cm³) D10D50 D90 D100 value angle Example 1 81 80 65 1.26 19.6 28.3 41.7 87.30.78 38° Example 2 70 81 57 1.03 10.5 16.6 27.1 61.9 1.00 56°Comparative 53 75 40 0.56 5.2 9.0 20.6 61.9 1.71 61° Example 1Comparative 84 75 63 1.42 17.0 49.3 82.8 244.7 1.33 24° Example 2Comparative 69 78 54 0.72 8.0 15.7 32.5 — 1.56 60° Example 3 Comparative82 77 63 1.36 14.2 36.8 62.1 — 1.30 29° Example 4

<Evaluation of Light Emission Characteristics of LED Using FluoridePhosphor>

The fluoride phosphor in Example 1 was added to a silicone resintogether with β-sialon green phosphor (trade name GR-MW540K,manufactured by Denka Company Limited). After defoaming and kneading,potting was performed in a surface-mount package to which a blue LEDelement with a peak wavelength of 455 nm was bonded, and furthermore itwas thermally cured to produce the white LED In Example 3. The additionratio of the fluoride phosphor and the β-sialon green phosphor wasadjusted so that the chromaticity coordinates (x, y) of the white LEDbecame (0.28, 0.27) in light emission during energization.

Example 4 was produced in the same manner as in Example 3, except thatthe phosphor in Example 2 was used instead of the phosphor in Example 1.Each white LED in Comparative Examples 5 to 8 was also produced in thesame manner as in Example 3, except that each phosphor in ComparativeExamples 1 to 4 was used. The addition ratio of the fluoride phosphorand the β-sialon green phosphor was all adjusted so that thechromaticity coordinates (x, y) of the white LED became (0.28, 0.27) inlight emission during energization.

<Evaluation of Variation in Light Emission Characteristics>

In Examples 3 and 4 and Comparative Examples 5 to 8, a white LED wasproduced 10 times in the same manner, and the light emissioncharacteristics (external quantum efficiency) of the sample obtainedevery 10 productions were measured to compare and evaluate variations inexternal quantum efficiency due to differences in fluoride phosphors.Table 3 below shows the luminance, the average value, and the standarddeviation of each white LED when the luminance of the white LED producedfor the first time in Example 3 is defined as 100. It was found thatExample 3 had higher external quantum efficiency and smaller standarddeviation at the time of 10 measurements as compared with ComparativeExample 5 and hence had little variation in quality and excellent andstable yield. In Example 4, the same excellent results as in Example 3were obtained. In all of Comparative Examples 5 to 8, the externalquantum efficiency was low and the variation was large.

TABLE 3 External quantum efficiency (455 nm excitation, unit: %) 1st 2nd3rd 4th 5th Example 3 100 101 100 102 102 Example 4 97 102 98 97 99Comparative 92 91 87 95 94 Example 5 Comparative 97 93 90 94 96 Example6 Comparative 95 93 92 88 96 Example 7 Comparative 94 91 95 98 98Example 8 Average Standard 6th 7th 8th 9th 10th value deviation Example3 101 98 98 102 99 100 1.6 Example 4 98 99 101 101 97 99 1.9 Comparative88 93 87 85 97 91 4.0 Example 5 Comparative 88 92 89 91 90 92 3.0Example 6 Comparative 98 89 94 88 85 92 4.2 Example 7 Comparative 91 9290 93 89 93 3.1 Example 8

It is found from the results of Examples and Comparative Examples shownin Tables 2 to 3 that the fluoride phosphor represented byA₂M_((1−n))F₆:Mn⁴⁺ _(n) of the present invention has the effect ofstably obtaining high external quantum efficiency when used as an LEDbecause both the bulk density and mass median diameter are in a specificrange. On the other hand, it is also understood that even only one ofthe bulk density and the mass median diameter is in a specific range,exhibiting no effect.

INDUSTRIAL APPLICABILITY

Using the fluoride phosphor represented by A₂M_((1−n))F₆:Mn⁴⁺ _(n) ofthe present invention for an LED may stably provide an LED having goodlight emission characteristics. The fluoride phosphor according to thepresent invention may be suitably used as a phosphor for white LED usingblue light as a light source, and may be suitably used for lightemitting devices such as lighting fixtures and image display devices.

1. A fluoride phosphor having a composition represented by a generalformula (1), a bulk density of 0.80 g/cm³ or more, and a mass mediandiameter (D50) of 30 μm or less:A₂M_((1−n))F₆:Mn⁴⁺ _(n)  (Formula 1) wherein 0<n≤0.1; an element A isone or more alkali metal elements containing at least K; and an elementM is a simple substance of Si, a simple substance of Ge, or acombination of Si and one or more elements selected from the groupconsisting of Ge, Sn, Ti, Zr, and Hf.
 2. The fluoride phosphor accordingto claim 1, wherein in the general formula (1), the element A is asimple substance of K and the element M is a simple substance of Si. 3.The fluoride phosphor according to claim 1, wherein the bulk density is0.80 g/cm³ or more and 1.40 g/cm³ or less.
 4. The fluoride phosphoraccording to claim 1, wherein the mass median diameter is 15 μm or moreand 30 μm or less.
 5. The fluoride phosphor according to claim 1,wherein a span value is 1.5 or less, as calculated by a formula (2)using a 10% diameter (D10) and a 90% diameter (D90) obtained from amass-based cumulative distribution curve and the mass median diameter(D50):(span value)=(D90−D10)/D50  (Formula 2)
 6. The fluoride phosphoraccording to claim 1, wherein a repose angle is 30° or more and 60° orless.
 7. A light emitting device comprising: the fluoride phosphoraccording to claim 1; and a light emitting source.
 8. The light emittingdevice according to claim 7, wherein a peak wavelength of the lightemitting source is 420 nm or more and 480 nm or less.
 9. The lightemitting device according to claim 7, wherein the light emitting deviceis a white LED device.